I just experienced this for the first time. Any special prep suggestions?

Depends who you are doing it with. I would never, EVER do it with someone who I am not VERY long term attached to. However, my hubby and I are pretty darned attached after 35 years of marriage and 5 years as lovers before that. We just shower well (often together, so a little finger/butt/soap play makes a nice warm up) and then we just "GO FOR IT". Tongue "fucking" is fun...but you never get in past maybe a half an inch or so, but that is okay...feels amazing. It is one of our favorite "69" things to do too.